Abstract: Disclosed herein is a disk drive in which servo-sector addresses are reproduced from a disk, a target data sector to be accessed is specified, and data is read from or written in the target data sector. The servo-sector addresses are recorded on the disk and randomized in accordance with a specific translation rule, thus arranged in an order different from the order they should be arranged in the same cylinder. The disk drive has a read head and a CPU. The head reads the randomized servo-sector addresses from the disk. The CPU refers to a back translation table, translating the servo-sector addresses back to the original servo-sector addresses. The CPU then checks the continuity of each servo-sector address with respect to the adjacent ones. If the servo-sector address has have no continuity, the CPU determines that the servo-sector address has an error.

Abstract: Properties of a compound semiconductor single crystal (e.g. GaAs single crystal) can be homogenized by subjecting the single crystal covered with a metal oxide powder (e.g. Ga.sub.2 O.sub.3 powder) to a heat treatment.

Abstract: A radiation detector containing as a scintillator a combination of two or more single crystals of cerium doped gadolinium silicate having different Ce concentrations, or a single crystal of cerium doped gadolinium silicate having different Ce concentrations therein, is improved in a spatial resolution and a time resolution.